Calorimetric apparatus



' April 15, 1941. E. x. SCHMIDT 2,238,606

I CALORIMETRIC APPARATUS Filed April so, 1958 s Sheets-Sheet 1 April 1941- E. x. SCHMIDT 2,238,606

CALORIMETRIC APPARATUS Filed April 30, 1938 3 Sheets-Sheet 2 April 1941- i E. x. SCHMIDT 2,238,606

CALORIMETRIC APPARATUS Filed April 50, 1938 3 Sheets-Sheet 5 TANK TEMPERATURE 60 65 TEMPERATURE RISE 3 22 .2 a

10 0 50 40 50 60 70 60 90100 PER CENT 01'' FULL SCALE HEATING VALUE.

PER cm or FULL SCALE EMT o\a8% 88 as 888 /10ZO3040506070500100 I FU L SCALE HEATING VALUE 9 QM twwxss PER CENT I .M L Mj Patented Apr. 15, 1941 2,238,606 GALORIMETRIC APPARATUS Edwin X. Schmidt. Whitefish Bay, Wis., assignor to Cutler-Hanmier, Inc., Milwaukee, Wis., acorporation of l jelaware Application April 30, 1938, Serial No. 205,259..

4Clairns. (01. 73-490) This invention relates to improvements in calorimetric: apparatus. .The invention relates more particularly to apparatus .for compensating for variations in temperature and composition of gas. in calorimetry.

A primary object of the invention is to provide improvedand simplifiedcalorimetric appa ratus; I

Another object is to reduce the cost of precision'typecalorimeters of the aforementioned character.

Another object is to provide. novel means for minimizing the'time lag'of response of calorimetric devices to variations in thequality or heatin value of the test gas.

Another object is to provide a calorimeter wherein the heat of combustion liberated in burning the test gas istransferred directly and eifectively. to a mixture of the products of combustion and excess air supplied to the burnerthe flow of air being. volumetrically proportional to the flow of test gas.

Another object is to provide such a calorimeter having novel means whereby the temperature rise produced in the mixture of combustion products and air- (which temperature rise will vary approximately in accordance with net heating value per cubic foot of gas) may be used as an accurate measure of the total heating value per unit volume of the gas.

Another object is to provide a calorimeter of the aforementioned character having novel means to compensate for variations in temperature,

pressure and saturation conditions of the test Another object is to provide means whereby the ratio of gas burnt to air supplied'to the burner is adjustable to a predetermined fixed value, depending upon the range of variation in heating value of the gas or gases for measurement of which heating value the particular calor rimeter is to be employed.

Another object is to provide apparatus for adapting a given form of calorimetric device and one type of scale and chart for gases of different compositions-with the=assurance that for the test gas for which the instrument has been adj usted a correct reading at one point in the scale will insure correct readings at all other points in the. scale.

Another object is to provide, in calorimetry, novel means for changing instrument calibration characteristics in order to compensate for differences in temperature rise factors at difierent points in the scale for different test gas compositions.

Another object is to provide pumping means of novel form for replenishing the calorimeter tank with liquid. 7 p 7 Other objects and advantages of the invention will hereinafter appear.

. The accompanying drawings illustrate certain embodiments ofthe invention which will now be described, it being understood that the embodiments illustrated are susceptible of modification in respect of certainstructural details thereof Without departing from the scope of the appended claims.

In the drawings, Figure 1 illustrates schematically and diagrammatically a calorimetric device'constructed in accordance with my invention.

Fig. 2 is an end view of a preferred form of the tank unit shown schematically in Fig. 1- the tank with its, cover, which forms the enclosing casing; being shown in vertical section.

Fig. 3- illustrates diagrammatically a modified form and arrangement of controlling and com pensatin elements adapted to function similarly to'those elements illustrated in Fig. 1.

Fig. 4 is a perspective view of the tank unit shown in Fig. 2.

Fig. 5 is a perspective view like that shown in Fig. 4, but viewed from the opposite side.

Fig. 6 is a perspective view of the enclosing casing, comprising the tank and cover shown in section in Fig. 2.

Fig; '7 illustrates diagrammatically a simple circuit employing a current type milliammeter as the indicating instrument for a calorimetric device-said circuit having my improved temperature compensating means included therein.

Figs. 8 and 9 each show curves representing values of E, M. F. expressed in per cent. of full scale M. Fpgenerated by the thermocouple'for different heating values of gases of different compositions, and

Fig. 10 is a curve illustrating variations in the value of the temperature rise as an incident to variations in temperature of the tank liquid.

It may be demonstrated, both theoretically and practically, that the temperature rise (and the E. M. F. generated by thermocouples subjected to the temperature rise of a calorimetric device of the character herein disclosed) will, with gas of any given composition, decrease if the tank temperature increases.

The decrease in temperature rise is due principally to the following factors: The amount of combustible delivered to the burner by the gas pump is reduced in density and, in addition, is reduced in volume by the increased partial pressure of the water vapor saturating the gas at tank temperature. The amount of dry heat absorb ing material in the products of combustion is reduced in like proportion to the reduction in the amount of combustible, but the water vapor which saturates both the air and the gas supplied to the burner increases with an increase in tank temperature, and increases the heat capacity of the products of combustion. Furthermore, the mean specific heats of all of the component parts of the products of combustion increase with an increase in tank temperature.

The combined effects of these various factors is shown graphically by the curve X of Fig. 10.

Thus if unity represents the temperature rise with a tank liquid temperature of 60 degrees F., the temperature rise for the same gas at 70 degrees F. tank liquid temperature would be .986;'

at 80 degrees F., .97; and at 90 degrees F. .95.

It is apparent that if the conventional type of millivoltmeter were connected to the thermocouple of a calorimetric device of the character herein disclosed, changes in tank temperature would cause changes in the instrument reading. Likewise it is apparent that, since the temperature rise is affected by a factor (not a fixed temperature difierence) the conventional cold junction compensation would not be suitable for making the instrument reading independent of tank temperature variations.

I have therefore provided special electrical devices and circuit connections for accomplishing the desired result. Referring to Fig. 1, which illustrates a preferred embodiment of the invention, the potential drop through resistor S and all of slide-Wire resistor S represents the potential or electromotive force generated by the thermo-couple (having the hot junction elements HJ and the cold junction elements CJ) when the calorimetric device is supplied with a gas having a heating value equal to the full scale reading of the instrument-as represented by the extreme right hand end of scale Ill. The potential drop across resistor S alone represents the E. M. F. 6 generated by the thermo-couple when the calorimetric device is supplied with a gas having a heating value of fifty per cent. (50%) of full scale reading.

The potential generated by the thermo-couple is balanced by a galvanometer G against the potential drop along resistor S and part of resistor S -contactor ll being automatically adjusted in the proper direction until no current flows through galvanometer G. In the conventional form of potentiometer millivoltmeter the current flow through the measuring slide wire resistor is fixed and made constant. With my arrangement, however, the current flow is made to decrease with an increase in the resistance value of a resistor RT, which is subjected to the temperature of the liquid in the tank 24 of the calorimetric device. This decrease in current flow is so related to the temperature of the tank liquid that a factor is introducedwhich decreases the current flow to substantially the same extent, or

degree, that the temperature rise (otherwise indicated by the calorimetric device) is decreased by a rise in temperature of the tank liquid.

The aforementioned variataion in the value of the current flow is effected in the following manner: Resistor RT is composed of a material having a positive temperature coefiicient of resistance, That is to say, an increase in temperature of RT results in an increase in its resistance value. Resistor RT may consist of a nickel thermometer wire, but it is to be understood that other materials, and other forms thereof, may be employed. The resistance value of RT should preferably be several times the combined resistance values of resistors S and S in series, to provide the desired degree of compensation.

Resistor R has a fixed resistance value. In

other words, it is not affected by changes in temperature; and it is preferably relatively low in resist-ance value, with respect to RT. A value of R equal to the combined resistance values of S and S in series, and equal to one-fourth of the normal resistance value of RT, is entirely suitable.

It is apparent that because of the relative values of the resistance R and the series circuit S, S and RT,- an appreciable change in the resistance value of RT will not substantially change the resistance of the parallel circuit containing resistance R For example, with the resistance value of R equal to the combined resistance values of S and S and equal to one-fourth of the resistance value of RT, a plus 8 per cent. change in the resistance value of RT will change the resistance value of the parallel resistor R only plus 1.01 per cent. In the calorimetric device herein disclosed I prefer to have a voltage drop across resistors S and S in series approximately equal to .03 volt; so that if the resistance value of RT is four times the resistance value of S and S the voltage drop across the parallel circuit is .15 volt.

By employing a dry battery 13 as a current supply for the potentiometer the remainder of the circuit must have a resistance value approximately equal to eight or nine times the resistance value of the parallel circuit. Inasmuch as this resistance value of eight or nine times that of the parallel circuit is unaffected by temperature, the value of the current flow from battery 13 varies only about plus .1 of 1 per cent. due to the change of plus 8 per cent. in RT and due to the change of 1.01 per cent. in the resist-ance of the parallel circuit. The voltage drop across the parallel circuit changes about plus 9 per cent, and the current flow through S, S and RT is reduced approximately 5 per cent.

Theoretically, there is one point in the resistor V'R. connected in series with the parallel circuit containing resistance R which is at a constant resistor R potential in relation to the point common to S (and S and R independent of variations in RT. This is the point at which the increase in potential drop across the parallel circuit is equal to the decrease in potential drop across the fixed By selecting proper values of resistance in resistors R S, S and RT this point can be made to give a potential difierence equal to that of the conventional standard cell, and the desired potential drop across S and S In practice it is not necessary to so carefully select the resistance values just mentioned as to have this point where the voltage drop will be exactly constant. Furthermore, a change in battery voltage will necessitate a change in total circuit resistance in order to establish the desired current flow, which will slightly change the point of exactly constant potential, Thus, with a change in fixed resistance of plus or minus 20 per cent. from the exact point of constant potential, battery current flow can be re-established with the standard cell within .02 per cent. of the cor- A rect value regardless of variations of as much as 10 per cent, in the resistance value of RT.

In the calorimetric device herein disclosed I provide for establishment of the desired value of current flow from the battery by burning a gas of known combustion characteristics, and adjusting the battery current, by means of an adjustable resistance or rheostat M, until a read ing. is obtained on the scale l (corresponding to the position of contactor II) which is equal to (or corresponds with) the theoretically correct reading for this particular gas. The. sliding contactor l5, associated with resistor VR, which connects with the standard cell 16, is then moved along its slide wire (resistor VR). while connected with galvanometer G through the medium of the down contacts l1, when bridged by the contactor I 8, of a manually operable push-pull switch (whose contactor is shown engaged with the up contacts [9).

Such movement of contactor l5 will eventually effect null indication on the galvanometer G, thus showing that the potentials have been balanced/ This point will approximate the position of contactor ll wherein the potential drop from the selected point of resistor S to the left hand end of resistor s is unafiected by variations in the resistancevalue of RT. The standard cell l6 may therefore be used to accurately adjust the current from battery l3 substantially unaffected by changes in tank temperature. l

v The circuit illustrated in Fig. 3 is in many respects like that shown in Fig. 1, and like parts have been given corresponding characters of reference in the two figures. In the device of Fig. 3', however, a. milliammeter is employed for setting or adjusting the current of battery L3. The circuit constants are similar to those described in connection with Fig. 1, and it is apparent that the battery current flow in Fig. 3 would vary slightly with a change in the resistance value of RT. As heretofore described, a plus 8 per cent.

change in the resistance value of RT would change the current flow minus .1 per cent. For practical purposes, this is sufficiently accurate-- but it is possible to furtherreduce this error by shunting the milliammeter 20 with a coil 21 made of wire composed of material having a positive temperature resistance coefiicientand subject ing such coil 2| to the temperature of the liquid in the tank 24 (Fig. 1); thereby eliminating all,

or substantially all, errors from this source.

In Fig. '7 I have shown a simple circuit employing a current type milliammeter 22 as the indicating instrument for a calorimetric device of the character herein contemplated. In this circuit the resistor RTwhich it is to. be understood is subjected to tank temperature-is composed of material having a positive temperature resistance coefficient. In the circuit of Fig. '7 resistor RT is relatively low in resistance value, as compared with the resistance Value of milliammeter 22, and as compared with the resistance value of resistor R Inasmuch as RT has There.-

fore, although an increase in the resistance value ofRT decreases the total current flow, the potential drop across the parallel circuit, including resistors RT and R increases, thus causing more current to flow through the milliammeter.

For example, if it be assumed that a milliammeter having a. resistance of the value of 5 ohms is selected, resistor RT will preferably have a resistance value of 1 ohm, and resistor R will preferably have a resistance value of '5 ohms. A change of plus 8 per cent. in the resistance value of RT' would cause the resistance of the parallel circuit, including RT and R to change. from .8333 ohm to .88816 ohm, or 1.064 3 times the original value of the resistance of said parallel circuit. The total circuit resistance would change from 5.8333 ohms to 5.88816 ohms-causing a change in total current flow from unity to 0.9907 per cent. thereof. The voltage drop across the instrument would then. be equal. to 1.0643 multiplied by 0.9907, or 1.0.545 times the value of the E. M. F. originally applied.

*With RT (Fig. 7) subjected to. the temperature of the liquid in tank 24 (Fig. 1), as represented by the dotted line rectangle 2 3 in Fig. 7,

the current flow through the instrument would be equal to 1.0545 times the originally applied E. M. F.,. which has been reduced by a factor of .95 by the change in tank temperature (under the assumed condition of a plus 8 per cent. change in the resistance of. RT); wherefore the value of the instrument current becomes 1.0545 times .95 or approximately 1.002 times the original value of such current. From the foregoing it will be apparent that if a high grade milliammeter 22 is employed the arrangement is such that the instrument is substantially unaffected by changes in the resistance value of resistor RT by changes in thermocouple E. M. F. resulting from changes in tank temperature.

The tank unit proper will be of similar construction for either the recording or the indicating types of calorimeter. The temperature rise, or difference between the temperature of the incoming gas and air and the temperature of the mixture of excess air and products of combustion, depends principallyupon the net heat input (exclusive of the latentheatof vaporization of the water formed in the combustion of hydrogen). It is also affected. to some extent by heat losses from the burner, difference in heat capacity of the products of combustion, differences in the amount of oxygen consumed, ratio of air to gas, temperature of the tank fluid, etc.

The relationship between temperature riseand these factors may be expressed by an equation:

1 T R (Net heating value per cu. ft. of gas) (Heat capacity per std. cu. ft. of air) A yre (F) 1; 1 .0012(A T) .0000l6(A T) or,

Total heating value per cu. ft. of. gas

Heat capacity per std. cu. ft. of air) In the above equations: D

R (in Equation. 2) is the ratio of net to total heating value per standard cubic foot of gas;

A/B: is the gear reductionthrough the change gears;

K is a constant, the value of which depends up"- on thecapacities of the gas meter and the air meter, and upon the interconnecting gearing exclusive of the change gears;

F isa factor depending upon the ratio of the heat capacity of a standard cubic foot of air and the mean specific heat of the mixture of excess air and products of combustion;

L is a factor depending upon heat losses from the burner; and

A is the difference between the temperature of the tank liquid, expressed in degrees F., and 60 degrees F.

Both of the equations just mentioned may be simplified by substituting a new constant C for constant K divided by the heat; capacity per standard cubic foot of air. When a therma -couple is used for measuring the temperature rise (the hot junction being located in the mixture of excess air and products of combustion, at a point directly above-but shielded from radiant energy ofthe flame; the cold junction being either subjected to tank temperature, or exposed to the stream of incoming air or gas), a potential is generated which varies almost directly as a function of temperature rise. Assuming inclusion of the slight divergence froma direct relation of generated E. M. F. and temperature rise in the factor L (both heat loss and divergence vary as a function of temperature rise), the E. M. F. generated by the thermo-couple at the temperature T of the tank liquid may be expressed as:

3. (E '11: (Net heating value) c (F) (L) (1.0O12(A T).OOO16(A T) or I 4. (E,,) =(Total heating value) (1%)( (1.0Ol2(A T).000 1 2 The last term in the above equations shows the effect of the temperature of the tank liquid on the generated E. M. F. The equation was derived empirically from calculations based on combustible displaced by water vapor in the test gas, and changes in the specific heat of the heat absorbing medium with a change in temperature. It may be apparent to those skilled in the art that by maintaining the temperature of the tank liquid constant, by either artificial heating or cooling, the effect of the last term might be eliminated. This is undesirable for several reasons;- principally manufacturing cost considerations, and practical difiiculties in maintaining heat transfers to and from the burner element stable, independent of variations in ambient (room) temperature. I have therefore introduced into the measuring instrument novel means for eliminating the effects of change in temperature of the tank liquid.

For a given tank unit the value of C is fixed by the mechanical design of the unit; R depends upon the composition of the gas; A/B depends upon the choice of change gears; L varies slightly with temperature rise; and F varies as the relation of net heat input to burner to air supplied to the burner changes.

In the design of the indicating and/or recording instrument, and in the standardization of the instrument for operation thereof on a particular kind of gas, I have provided methods of and means for eliminating errors in the direct indicating and recording of heating values, which errors would be present if the several variable factors mentioned in the foregoing equations were not compensated for. The arrangement is also such that printed charts and scales can be adapted to approximate a number of scale distribution characteristics, as required by test gases of different combustion characteristics. That is to say, wherein there are different values for the factor F for the same heating values per cubic foot.

Referring to the curves shown in Figs. 8' and 9, curves A, B and C represent values of E. M. F. expressed in per cent. of full scale E. M. F. generated by the thermo-couple for different heating values of three gases of different compositions. The differences between .the curves have been exaggerated to some extent in order to make the description more clear. The differences between curves A, B and C at per cent. of full scale E. M. F. are due to the differences in temperature rise in the calorimeter resulting from differences in gas composition at full scale and at half scale; namely, factors F1 and F5, respectively.

For example, when burning a mixture of propane gas and air in this calorimeter, with a properly selected air to gas ratio, the relation between generated E. M. F. and gas heating value is practically a straight line (line B). Nevertheless, we know that the temperature rise factor (F5) of such mixture at 300 B. t. u. heating value is 1.0185 times as great as the temperature rise factor (F1) at 600 B. t. u. If we now substituted 2. carbureted water gas whose heating value varied from 300 to 600 B. t. u., the temperature rise factor would be 1.023, and the curve would be above the line B at 50 per cent. of full scale heating value (curve C).

Referring to Fig. 8; assume that we have a potentiometer type recorder with a scale graduated from 50 per cent. to per cent. of the full scale value. It is obvious that by changing the value of the current fiow through the potentiometer, we can make a 4 ohm slide wire, corresponding to the scale from 50 per cent. to 100 per cent., have a potential drop of 53 per cent. of full scale E. M. F. for curve A, 50 per cent. for curve B, and 47 per cent. for curve C. The current through the potentiometer is thereby fixed. In order to set up potential corresponding to a heating value from zero to 50 per cent. of full scale, it is merely necessary to provide a resistance of the proper value in series with the po tentiometer slide wire. That is to say, resistances S respectively having values of: 3.55 ohms for curve A, 4 ohms for curve B and 4.51 ohms for curve C.

Referring again to Fig. 8, and assuming that curve B represents the relation between heating value and E. M. F'. for a gas whose temperature rise factor is the same at both 50 per cent. and 100 per cent. of full scale value. Then, in order to agree with curve C, gas C must have a composition such that Similarly, gas A must have a composition such that Inasmuch as it is desired to make the 4 ohm slide wire E. M. F. correspond to 50 per cent. to 100 per cent. of .full scale heating value; for curve B, S=4 ohms; for curve A, S must equal or 3.55 ohms; and for curve C, S must equal or $51 ohms. For all curves 'S may be expressed in terms of S as:

As heretofore pointed out, .curve A has been drawn with reference to curve B in ;a manner to exaggerate the differences met with on commercial gases. As also pointed out, due to minor heat losses, .thermo-couple characteristics, etc,

with .a mixture of .propane gas and air having .a

value .of .from .300 B. .t. u. 110.6003. 1 '11.,'wi.1ih

fied to read:

By substituting the values of --F-.5 and F1, calculated for .a mixture of propane gas and air, S:coil-is to be designed fora resistance value of:

In order to adapt the instrument .-for .useon carbureted-water gas, it is merely necessary to design S for:

7 or L000 S With the value .of .S chosen in the manner aforedescribed, adjustment. of ;the:potentiometer current to provide a correct readingof theinstrument at any one pointin .the scale wilhfor all practical purposes, insure correct readings thereof at all other .points in the ,scale. Inasmuch as the differences in curvatures. ofzthe lines for different gases are slight, it .is possible to use a standard chart for different .kindsofga-ses without introducingappreciable errors.

A similar result may be attained when employing a potentiometer having .a suppressed zero, by providing for. shifting of 'the .efiective slide wire to the required degree .with relation to the scale. In like manner, a milliammeter may be employed, by providing for-shifting of the zero of the instrument .to the :required .de-

gree.

Referring now to Fig. 9; curves.A,iB-and .C

are similar to the like designated curves.:in Fig.

8. Assuming that a. milliammeteris .employed to indicate heating value. of .angas :whichphas a straight line; relationship betweenxheating "value andvapplied @E. so .thatithe:instrumentiollows cu v '13- 30 ap y he e in m t and scale to measure heating value of a gas corresponding with curve C the following procedure is followed: For curve C a gas having a heating value corresponding to 50 per cent. of full scale heating value results in 53 per cent. of full scale E. M. Inasmuch as the top half of the scale .(50 divisions from 50 to per cent. of the full .scale heating value) should therefore represent 47 per cent. of the total E. M. F., the instrument deflection corre ponding to a. heating value from zero per cent. to per cent. should equal or 56.383 divisions giving a dull deflection of 50+56.383 or 106.383 divisions. If the mechanical zero of the instrument is set at 100--l06.38-3

divisions from zero (6.383 divisions below zero on the scale) and the circuit resistance changed so that at full scale heating value full scale reading.

is obtained, the instrument will read substantially correct over the range of 50 to 100 on the scale. Similarly, for curve A the mechanical zero should be set at or 5.66 divisions above zero on the scale to give substantially correct readings over the .top half of the scale. A general equation may be written in terms of F1 and R5 for the amount of mechanical zero shift to provide the desired compensation, namely:

A negative value indicating that the mechanical zero should be set below zero. Converting this equation to actual conditions determined experimenta'lly the equation assumes the form: Mechanical zero setting:

For carbureted water gas:

.55 devisions below zero For a potentiometer in which the relative positions of scale and slide wire can :be changed a similar efiect maybe produced.

The means aforedescribed permit adapting commercially available instruments and one type of scale and chart forgases of different compositions, with the assurance that for the test gas for which the instrument has been adjusted or i calibrated acorrect reading at any one point in the scale'will insure correct readings at all other points in the scale.

In accordance with my invention the calorimetric device is standardized that,is,, made to read correctly at onepoint in the scale) by burning a gas of known heating value and combustion characteristics; calculating the reading which this gas should give in order to read correctly on the particular gas for which the-calorimetric device willbeused; and adjusting the device so that it' will produce the desired reading. -I have also included in the potentiometer type of instrument (Figs. 1 and 3) auxiliary means for checking and resetting the potentiometer currents without having to resort to the complete standardization procedure of burning the standardization gas. Standardization on gas will ordinarily consist in burning hydrogen as the test gasalthough other gases of known combustion characteristi'cs are satisfactory. The calorimetric device is preferably so constructed that at full scale reading approximately 22 net B. t. u. will be delivered to the burner for each cubic foot of air (primary and secondary) supplied. The gas and air meter capacities and the gearing are selectedso that the volume of gas is equal to times the volume of air; where the drive of the gas meter.

It is preferable to use hydrogen (whose combustion characteristics, although differing materially from other gases, are better known) as a is the ratio of the drive-driven change gears in I12};

standardization gas, with change gears whichti-g'o will give a reading close to the top of the scale.

change gears provide the desired reading, liberating approximately: 7

with carbureted water gas of 300 to 600 B. t. u. For this service change gears are employed-the same providing for liberation of:

(.083) (600) (.9218) =22.9 net B.t.u.

per cubic foot of air at full scale, and

(.083) (@em) (.9194 =11.3 net Btu.

per cubic foot of air at 50 percent. of full scale. The temperature rise factors for carbureted water gas, based on total heating value, are, at

, full scale (F1) =.8'74; and at half scale (F) =.894.

The approximate reading on hydrogen will then 40 Y .934 x yzcac 577 At 577 B. t. u. on the scale the temperature rise factor is somewhat larger than .874 used in the above approximation, namely,

' measuring circuit.

The theoretically correct reading on hydrogen then becomes:

30 40 .934 x yzeae -575.7

By adjusting the instrument to give the above reading on hydrogen (on the potentiometer type, by adjusting the current flow; on the milliammeter type, by adjusting the instrument resistance) the instrument will read correctly on carbureted water gas over a range of 300 B. t. u. to 600 B. t. u. per standard cubic foot.

With reference to compensation for variations in temperature of the tank liquid: Equation 4. giving the relationship between the generated E. M. F. and the temperature of the tank liquid, includes the term (1.00l2(AT) -.000016(AT) that is to say, the generated E. M. F. decreases as: the tank liquid increases. If the generated E. M. F., with a. tank liquid temperature of 60 degrees F., is taken as 100 per cent; then the generated E. M. F. is:

100 per cent. at 60 degrees F.; 98.3 per cent. at '75 degrees F.; and 96.3 per cent. at degrees F.

By employing a potentiometer recorder or indicator for measuring the generated E. M. F. arranged in a manner so that current through the potentiometer decreases substantially in accordance with the relationship just mentioned, the potentiometer reading will be unaffected by variations in generated E. M. F. resulting from variations in tank temperature.

Referring more specifically to Fig. 1, which shows a preferred arrangement for accomplishing the desired results. S1 is a slide Wire resistance, corresponding to a scale of heating value from 50 to per cent. of full scale. Connected in series therewith on the left is a resistor S and on the right is a positive slope resistance thermometer .RT made of pure nickel or other suitable material. Paralleling S, S1 and RT is the fixed resistance R1. An adjustable resistance 14, adjustable resistance VR, and dry cell l3 complete the circuit through which the potentiometer current flows. The hot junction HJ of the thermocouple, subjected to the temperature of the products of combustion, together with the cold junction CJ, subjected to the temperature of the tank liquid, and the galvanometer G, complete the Resistance thermometer RT is also subjected to the temperature of the tank liquid. To obtain a reading on the potentiometer, contactor II is moved along resistance S1 until no current flows through the galvanometer G.

It is possible to obtain the desired relationship between the value of current flow through S and the temperature of the tank liquid by employing various different values of S, S1, R1 and RT; but I prefer to make S ,.S1 (combined) and R1 of equal resistance values. I also prefer to use a conventional dry cell l3 for supplying current to the potentiometer. It is apparent that if R1 is made excessively large, with respect to S, S1, the desired results cannot be obtained. There are also definite objections to making R1 very small with respect to S, S1. The choice of R1 approximately equal to-S, S1 has advantages when a potentiome ter recorder is used in which a standard cell is is used for standardizing the potentiometer.

For the purpose of simplifying the calculations, it is assumed that in the potentiometer recorder disclosed in Fig. 1 the resistance values of S, S1 (combined) and R1 are exactly equal; but i is W und r to d ha t 'resisteec values of S 5i (combined) and Rimight difier somewhat 'with respect to eachother without appreciably affectingthe results; "Equations 1 and 2 for temperature rise of the calorimetric device, and Equationsli and 4 for generated E. Mrll 'include the term (1-.0012(AT)--.000Q16(AT) Expressed in a difierent manner; if the generated E. M. F. at 60 degrees F. temperature of the tank liquid is taken as 100 per cent, then: Egat' '75 degrees F.=98 .3 percent.) and E3 at 90 degrees F.=96.3 percent.

The resistance of a pure nickel thermometer maybe expressed as:

RTT=RT60(1+.0026 (AT) +.0000( 11 75 (AT) Expressed in a different manner; if the resistance of the thermometer at 60 degrees F. is equal to BT60, then the resistance at '75 degrees 39 7 L nd. the r sistance t 9 e.- sres F;- 1 .079e(n:rs A il t e? S, =R Qhms; t a t volt e 01 dry cell 13 volts, and. that it id t that. 1. sse see ent :3 m llivolts wss 'fslide wir 5. -9. a s ide Wire re o .0035 m er w th t e. ank i ui at separ te. i 59 de rees. f. Thev cu rent.

he de ir d lat ps stwe a t e curre t s.

a -"de ees"???- n; 99fi sres E-I s ush a th fq d. as in. sweet wi neutr lize h decrease "in g nerated E. M. Ff. caused by an instat me ts '65 e rees and at. 90 e r es I, at degreesF. I -a't QO deg rees F. 9:

shesl e al r 3.84

r at equal s ts: ohms at 6p degrees Loser dredths F. givesthe following potentiometer currents in S and'sli'de'wire Sif,andtota1currents:'

Tani; liquid temperature 010 degrees F., current in S1=.0O3 5 amp.=100 percent. Total ammeter current=,01 329=100 per cent.

Tank liquid temperature '75 degrees EL, current in S, S1 )O3j434 amp.=- 98.13 per cent. Total ammeter current=.013286 =99.9 6 per cent.

Tank liquid temperature 90 degrees F., current in S S1 .0 03367 arnp.= 96.3 per cent. Total amrneter' current=.01 3281 '99.93 per cent.

The foregoing tabulation shows that although the desired current relationship is obtained in S and slide wire S1 the total current passing through the adjustable resistance l4 varies only slightly-so that for all practical purposes the adjustable resistance l4 might be used as an index for stabilizing potentiometer current. The effect of temperature of the tank liquid upon the parallel circuit (R1 in parallel with S, S1 and RTresistances) is'as follows: At 60 degrees F.=5.8923 ohms; at degrees F.=5.9345 ohms; and at degrees F.=5.9688 ohms.

The current (total) is approximately .0133 ampere, so that the resistance for an In drop of 1.0186 volts (Voltage of a standard cell) would be approximately 7'? ohms. By utilizing, the voltage drop of the parallel circuit, plus enough of VR to provide 1.0186 volts for standardization, the increase in resistance of the parallel circuit and the decrease in the total current (both resulting from the increase in tank temperature); tend to neutralize each other so that the potentiometer current can 'be' standardized by useof a standard-cell. As a result of the change from 60 degrees F. to 90 degrees F. the parallel resistance increased .0765 ohm, which is approximately one-tenth of 1 per cent. of 7'7 ohms. The current decreases approximately seven-hunof 1 per cent., or: 1.001 times .9993=1.0003.

The foregoing calculations, are based. upon a battery voltage of 1.45. With a new dry, cell l3 the voltage will be more nearly 1.6 volts-requiring a value of VR of 114.52 ohms to provide the desired current. With abattery about due for replacement the voltage would be in the neighborhood ofl 1.2'volts, requiring a'VR value of 9-1.'95-' ohms." No other changes are required in the cir 1 cuit, the compensation for temperature of the tank liquid and standardization of potentiometer current remaining the same.

For certainapplicationsitis desirable to use a milliammetenof the current type, instead of the more complicated and more expensive'potentiometer type instrument. I have therefore devised methods of and means 'formaking the,

reading of a milliammeter independent of variations resulting from variations. in generated E. M. F. incident to; variations. in temperature of the tank liquid. Thus, referring to Fig. 7, 22 represents a commercial form of milliarnmeter the resistance value (R1, not shown) of which is substantially independent of variations in temperature, and the indication of which'is also sub- The compensation thermometer RT, subheretofore set ifcrtnl T'Ifh'at. toi 's'a' fir Since A1 should be the same at 60 degrees F. as at 90 degrees F.:

W w) (1.07% 13,113, +R1R2 1.0397 GO( 1.0796 R, +132) +RIR2 l.0397(R R .0399(RT60) R1 R2 RT (.0397 12.12, R112.

At 60 degrees F. the resistance of the parallel circuit is:

(RTBO) 1) 60+ l If milliammeter 22 gives full scale reading on 5 millivolts and the generated E. M. F. for full scale reading at 60 degrees F. is 30 millivolts, then:

ao) (R1) oo) 1) RT +R1 RTao l Substituting the value of R2 in the equation for BT60! 1 R or R 2 RT R 2 RT 2 5 R 1+( so)( i) to) X9856) (ROHRTGO) 6 1) so) 1) eo) 0 If R1=1 then RTsn=.6625 and R2=1.9917 parallel resistanceat 60 degrees F.=.3983. Total=2.390 total current at .030 60 degrees F. .0l25 amperes If the resistance of the milliammeter were 25 ohmsmillivolts or .002 ampere'for full scale,

then RTe0=16.56 ohms, and R2=49.79 ohms for the desired compensation effect and reading.

It is apparent from the foregoing that a greater or lesser proportion of the generated E. M. F. may be utilized across the instrument and still maintain the desired compensation. For example, if an ammeter is selected which gives full scale reading on 10 millivolts, then by designing:

&ZE .492) (R1);

and t (3) (R R2 m- -972R1 It is also apparent that there is a limiting value of the ratio of instrument millivolts for full scale to generated E. M. F. beyond which it is not possible to go. This limiting value is at which condition RTeo calculates out at zero. An instrument is therefore chosen which will provide values of resistances for various parts of the circuit which will give a practical arrangement. A 10 millivolt-.0002 ampere-50 ohm instrument is ideal for the purpose.

Referring more specifically to the particular form of calorimetric device herein disclosed, it is to be understood that the same consists essentially of two unitsa tank unit or calorimeter proper, designated in general by the numeral 24, where the heating effect of the gas is measured, and a recording instrument, designated in general (Fig. 1) by the numeral 25, for translating the heat measurement into total B. t. u. per standard cubic foot of test gas, independent of variations in temperature, pressure and humidity (saturation) The heating value of the test gas is ascertained by imparting the heat of combustion obtained from the combustion of the test gas to a mixture consisting of excess air and products of combustion, and measuring the temperature rise of the mixture. The streams of test gas and air are supplied to the burner in fixed volumetric proportions by measuring devices, such as pumps 26 and 21, respectively (Figs. 1 and 2), which are connected to each other by gearing 28, 29 and driven by a motor 30. Not only are the volumetric rates of delivery maintained in fixed proportionality to each other, but this proportionality is efiected while maintaining like conditions of temperature, pressure and humidity of the test gas and air by means of a common water seal 3| for the motor driven pumps or meters 26 and 21.

The test gas is burned directly in and with the metered air in burner 32, and inasmuch as the products of combustion mix with the excess air to form the heat absorbing medium, the temperature increase over that at which the air and gas were supplied is used as an indication of the heating value. This temperature increase varies almost directly in accordance with the net heat input (as distinguished from the total heat input,for the latent heat of vaporization of the water formed in combustion is not released). Nevertheless, the calorimetric device herein disclosed is preferably calibrated to read in, or indicate, the total heating value per unit volume of the test gas.

The reading of the calorimetric device depends to some extentupon gas composition, in addition to the heating value, and for certain applications may introduce objectionable errors if used on gases other than those for which it has been standardized.

The test gas is piped to the tank unit where it passes through a small orifice nipple 33, into the inlet pipe 34. The upper part of pipe 34 connects with the bleeder burner 35, which is open to atmosphere, and the lower part of pipe 34 connects directly with the inlet end of gas meter 26. The orifice nipple 33 is adapted to limit the flow of gas to about three cubic feet per hour, and inasmuch as the comparatively large opening through the bleeder burner 35 to atmosphere prevents any pressure from building up in the inlet pipe 34, the gas is metered by meter 26 at atmospheric pressure, and the water level on the inlet side of meter 26 is at the same level as the water in the tank 24. The gas meter 26 is driven by motor 30 with built in speed reducing gearing 38 through the medium of change gears, designated in Fig. 4 by numerals 31, 38, 39 and interposed idler 40,gear 39 being attached to the gas meter 26. The air meter 21 is driven from the same motor 39 and speed reducing gearing 36, through pinion 4|, driving spur gear 42, which is fastened on the shaft of air meter 21.

Both the gas and air meters 26 and 2'! are of the multiple compartment type, so constructed that when they rotate they take in, seal off, and discharge fixed volumes of gas and air, respectively, into their discharge chambers. ters are likewise so constructed that the gas and air are pumped at approximately uniform or constant volumetric rates.- Both meters, the complete motor drive, and the burner structure are mounted on the same main base casting-as shown at 43 in Figs. 4 and 5. In operation, base casting 43 is mounted on the tank 24 which is partially filled with water--the water providing a common seal for both meters and also having a temperature equalizing effect.

The outlet 44 of the air meter 21 has connectors 45 and 46; the outlet 41 of the gas meter 26 has one connector 48. These connectors rise above the level 3| of the water and provide simple leaf-proof water sealed connections which can be conveniently opened for inspection. Similar water sealed connections are made with the pipes at the bottom of the burner 32. Thus, pipe 49 connects with the bottom of the central burner tube 50; and pipe 5| connects with the passage f 52 between central tube 59 and combustion tube 53. Most of the air from the air meter passes through connector 45 into pipe 5|, thence upwardly inside of the combustion tube 53 (Fig. 1) where it meets the flame 54 and furnishes secondary air of combustion. The remainder of the airprimary air from air meter 2'|passes through connector 46 into connector 55. The test gas also enters connector 55, mixes with the primary air, and goes into pipe 49. Combustion takes place at the top of the central tube 50 of the burner.

The products of combustion mix with the excess air to form the heat absorbing medium. The heat absorbing medium passes into intimate contact with the hot junction HJ of the thermocouple. Some of the mixture then passes through holes 56 (Fig. 1) in the thermo-couple cap 51 to atmosphere and the remainder passes down the annular passage 58 formed by the return fiow bafile 59 and then up through openings 60 to atmosphere. The cold junction CJ of the thermocouple is positioned within a cup or cylinder 6|, adjacent to the bottom of the latter. Cylinder 6| (Fig. l) is partly submerged in thctank Water These me- 3|. This cylinder also contains the aforedescribed compensation thermometer RT.

The electromotive force generated by the difference in temperature between the hot junction HJ and cold junction CJ is a measure of the heating effect of the test gas. It is this electromotive force which is translated into heating value in the recording instrument.

The water level in the main tank 2i (Figs. 1 and 2) is maintained by an oscillatory pump comprising a cup 62 having an angular upper edge 63 (Fig. 4)--said cup being carried by and communicating with a pipe or tube 64 bent to substantially L-shape. The short-end portion of tube 64 overhangs the main portion 24 of the tank, for discharging into the latter, as shown in Figs. 1 and 2. The tube 64 is supported by a metal member 65 which is pivotally supported by pin 66 (Fig. 4) carried by a bracket 61, which may be attached to the tank wall. Member 65 is provided with a long arm 65 (Fig. 4), the lower edge of which is engaged by a roller 68 supported by screw 69, which is fastened to and movable with gear 42. Cup 62 and tube 64 are thus alternately, raised and lowered during rotation of gear 42. The cup 62 picks up water from the auxiliary tank 24* and drops a few drops thereof into main tank 24 during each complete rotation of gear 42. to replace evaporated water, flows over the overflow weir 16, as shown in Fig. 1, thereby maintaining a constant water level in the main tank 24 As aforeindicated, the recorder herein employed is of the self-balancing potentiometer type with cell [6 and the rheostat 14 adjusted by hand untilthe proper current is flowing.

The electromotive force generated by the thermocouple in the tank unit is applied across the battery terminals, through the galvanometer 'G and switch IS in the upper or run position thereof, wherein contacts l9 are bridged. contact II is moved along resistor S until the galvanometer G returns to the balanced position, indicating that the potential drop through S and part of S is equal to the electromotive force generated in the thermocouple.

arranged to automatically move slider H (and indicator and recorder 12) to the balancing position.

The portion of the battery voltage used in checking the potentiometer current is the voltage drop across S, S and the compensation thermometer RT in series, paralleled by resistance R the whole parallel circuit being in series with resistance H and a portion of rheostat VR. The portion of VR included for the checking of the potentiometer current is determined immediately following standardization of the calorimetric device on hydrogen, and the position of contactor 15 of rheostat VR remains fixed until a subsequent hydrogen test indicates the need for a change in this setting.

The excess water, over that required Defiections of, galvanometer G are amplified mechanically and The resistance of the compensation thermometer RT changes with variations in temperature of the tank liquid, and changes the value of current flowing through resistance S and slide wire resistance S but does not appreciably affect the flow of current from battery 13. The change in current flow through S and S corresponds substantially with the variation in the electromotive force generated in the thermo-couple, so that the position of indicator and recorder 12, that is, the instrument reading, is unaffected by changes in tank temperature. Since the current flow from battery I3 is substantially unaffected by changes invalue of the compensation thermometer resistance RT, and since the change in resistance across which the potential drop is measured when standardizing is very small, standardization may be effected independently of tank temperature over the entire operating range of the instrument; namely, 60 degrees F. to 95 degrees F.

The calorimetric device is standardized by burning a sample of pure hydrogen, Whose heating value per unit volume and combustion characteristics are well known-a special set of hydrogen test gears (not shown) being substituted for the gears 38, 39, 40 (Fig. 4) to thereby provide a reading at a point on the scale l (Fig. 1) where the accuracy of the reading is best. The recorder circuit is then adjusted so that a reading is obtained which will assure correct reading on the particular gas for which the instrument is being standardized. With a fair knowledge of the approximate composition of the particular gas, standardization on hydrogen insures accuracy of the calorimetric device throughout its total range of operation.

What I claim as new and desire to secure by Letters Patent is: r

1. In a calorimetric device, in combination, a burner, means for continuously supplying to said burner under the same temperature, pressure and saturation conditions constant volumetrically proportioned flows of test gas and air to support combustion of said test gas, the heating value per unit volume of said test gas being subject to relatively wid variations, a potentiometer type measuring instrument, a thermo-couple having hot and cold junctions, one junction of said thermo-couple being subjected to said temperature condition, the other junction of said thermo-couple being subjected to the thermal effect of combustion of said flows of gas and air, whereby an electromotive force substantially proportional to the temperature difference between said hot and cold junctions is generated, and means including a positive temperature coefficient resistor in circuit with said thermocouple for changing the value of the current flow through the measuring portion of said calorimetric device as an inverse function of variation in value of said temperature condition, said last mentioned means being adapted to change the calibration of said calorimetric device in a manner to effect multiplication of the reading of the latter by a factor which is a function of the changes in temperature rise resulting from variations in said temperature condition, to thereby accurately compensate, over the entire measuring range of the calorimetric device, for all variations in value of said temperature condition.

2. In a calorimetric device, in combination, a burner, means for continuously supplying to said burner under the same temperature, pressure and saturation conditions a volumetrically constant flow of test gas and a volumetrically proportional flow of air in excess of that required to support complete combustion of said test gas, the heating value per unit volume of said test gas being subject to relatively wide variations, a potentiometer type measuring instrument, a thermo-couple having hot and cold junctions, one junction of said thermo-couple being subjected to said temperature condition, the other junction of said thermo-couple being subjected to the thermal effect of combustion of said flow of gas in the presence of said excess flow of air, means for effecting a reflex flow of the products of combustionand the excess of air in ja-cketing relation to the point of heat transfer to minimize heat losses, whereby an electromotive force substantially proportional to the temperature difference between said hot and cold junctions is generated, means including a positive temperature coeflicient resistor in circuit with said thermocouple for changing the Value of the current flow through the measuring portion of said calorimetric device as an inverse function of variation in value of said temperature condition, and said last mentioned means being adapted to change the calibration of said calorimetric device in a manner to effect multiplication of the reading of the latter by a factor which is a function of the changes in temperature rise resulting from variations in said temperature condition, to thereby accurately compensate in the determinations of said calorimetric device for all variations in value of said temperature condition throughout the total range of test gas heating values for the determination of which said calorimetric device is adapted.

3. In a calorimeter of the character wherein a volumetrically constant flow of test gas and a volumetrically proportional flow of air at the same temperature and pressure as said test gas, and in excess of that required to support complete combustion of said test gas, are subjected to combustion and wherein the products of such combustion are combined with the excess of such flow of air to form the heat-absorbing medium, in combination, means for standardizing the calorimeter reading by burning a volumetrically constant flow of a standard gas of known combustion effect and known heating value per unit volume to produce a reading, said means including a potentiometer type measuring instrument comprising a source of current of substantially constant potential, a manually adjustable rheostat for controlling the flow of current from said source, circuit portions of comparatively low resistance and comparatively high resistance, respectively, connected in parallel relationship to each other across said source, said last mentioned circuit portion including a measuring element the resistance value of which is substantially unaffected by temperature and an element the resistance value of which changes with variations in temperature, said last mentioned element being so related and arranged with respect to the element unaffected by temperature and to said circuit portion of relatively low resistance as to affect the current flow through said measuring element in a manner to change the calibration of the measuring instrument as an inverse function of any change in resistance value of said element which is affected by temperature, to thereby insure correct actual readings expressed in standard units of heating value per unit volume when said calorimeter is operated through out its total range on gases having combustion effects in relation to heating values perunit vole s stantia ly d ferent from that of said standard gas of known combustion effect and known heating value per unit volume.

4. In a calorimeter, in combination, a potentiometer type measuring instrument comprising a source of direct current of substantially constant potential, a rheostat for con-trolling the flow of current from said source, a parallel circuit including a circuit of comparatively low resistance and a circuit of comparatively high resistance, said last mentioned circuit including a measuring portion substantially unaffected by temperature and a. portion whose resistance changes with variations in temperature, a galvanorneter, means for connecting said galvanometer across different parts of the measuring portion of said circuit of comparatively high resistance and for changing the position of one of said connecting means to produce null reading on the galvanometer, and said portion of the circuit of comparatively high resistance which is affected by temperature being so related and arranged with respect to the portion thereof unaffected by temperature and to said circuit of comparatively low resistance as to affect the current flow through the measuring portion of said circuit of comparatively high resistance in a manner to change the calibration of the measuring instrument as an inverse function of the change in resistance of said part of said circuit of comparatively high resistance which is affected by temperature, to thereby accurately compensate, over the entire measuring range of the instrument, for all variations in temperature rise resulting from said first mentioned variations in temperature.

EDWIN X. SCHMIDT.

Certificate of Correction Patent No. 2,238,606. April 15, 1941.

EDWIN X. SCHMIDT It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as foil owe: Page 4:, first column, line 11, for A read AT; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the casein the Patent Oflice.

Signed and sealed this 16th day of September, A. D. 1941.

HENRY VAN ARSDALE,

Acting Oomvm'ssioner of Patents. 

